The success of HIV antibody tests in narrowing the window period of HIV diagnosis has been notable. However, immunoassays designed to detect antibody alone will not be able to identify individuals with acute infection who have not yet begun to produce HIV-specific antibodies. Attempts to detect acutely infected individuals have mostly involved RNA detection algorithms used on pooled HIV antibody-negative specimens. However, the use of RNA-based detection methods is expensive, laborious, and can be operationally daunting. An alternative to the detection of acute HIV infections using RNA-based methods is to utilize antigen-antibody combination tests, also known as fourth-generation immunoassays. Fourth-generation immunoassays have recently been cleared by FDA for use in the US. These fourth generation assays have multiple shortcomings: a) the detection limits for p24 antigen is still not low (~ 15 pg/mL) and b) the assays are run on large, expensive, cumbersome and time-consuming clinical chemistry analyzers. The assay results are not immediately available to the patient. The specific aim of this proposal is to, develop a reliable, accurate, cost-effective Point-of-care (POC) ultra-sensitive quantification of HIV p24 antigen with detection limits in range of sub pg/mL. This test could significantly reduce the serological window for detection of HIV and provide results to the patient in a timely manner.